Ice making machines and chillers are well known. These types of machines are used in a number of industries including the food processing, plastics, fishing, and general cooling applications. Chillers cool liquids generally to a point above their freezing temperature, while ice making machines generally cool water or a solution below its freezing point. Ice machines and chillers use a heat exchanger that is generally cooled by refrigerant that flows through internal passages. Water, or any other liquid to be cooled, is introduced onto the surface of the heat exchanger. If the liquid is frozen, a variety of methods are then used to remove the ice from the heat exchange surface, including using a scraping device, or heating the surface temporarily to release the ice. Slurry ice differs from flake ice in that the water that is frozen usually has mixed with it salt, or some other substance, for altering the freezing point. The resulting slurry product has a slush consistency and may be pumped, making it preferred for many applications where the end product must be conveyed. Furthermore, its energy storage and transfer characteristics are superior to other types of ice.
U.S. Pat. Nos. 5,157,939 and 5,363,659 by Lyon, as well as U.S. Pat. No. 5,632,159 and U.S. Pat. No. 5,918,477 by Gall disclose heat exchangers in the shape of a disk with internal passageways for the refrigerant to travel along the interior of the disk. The disk rotates in contact with a fixed scraping mechanism which removes ice formed on its surface. In Lyon the disk is formed with two mating disk halves, each of which includes a plurality of grooves on its internal surface. The pattern of the grooves in the two halves are mirror images, so that when the halves are mated and brazed together, corresponding grooves mate to form passages. The manufacturing of this heat exchanger involves chemically etching each separate half of the disk, which is expensive.
The two devices by Gall disclose a heat exchanging device that is formed by cutting fluid passages into a thick metal plate using a milling machine. Once the passages are cut, a thin flat plate is joined to the milled plate to complete the disk. Although milling the plate is not as expensive as chemically etching it, and in this process only one plate is being machined as opposed to both, this is still a lengthy and expensive process. In the prior art flat disk heat exchangers, the refrigerant does not come into contact with a significant portion of the heat exchange surface. The reason for this is that there needs to be sufficient material between the channels to provide a large enough surface area for brazing in order to withstand pressure.
The refrigerant in heat exchangers disclosed in prior art is introduced into the heat exchanger through a single inlet and removed through a single outlet. The refrigerant is driven by the compressor through the internal passages. There is an optimal range of velocity for the refrigerant: If velocity is too small, the heat transfer efficiency decreases, and there will not be sufficient velocity to carry oil, which is picked up from the compressor, back to the reservoir of the compressor. If velocity is too large, the compressor will waste energy.
Having a single inlet and single outlet forces all of the mass of the refrigerant to pass through a small cross sectional area. For a fixed mass flow of refrigerant, a smaller cross sectional flow area corresponds to a larger velocity. Thus, by having a single inlet and outlet, the channel length and the velocity are increased, and therefore the work of the compressor which moves the refrigerant in the ice machine system is significantly increased. In the heat exchanger of the prior art, the only way to reduce the refrigerant velocity is to increase the cross-sectional area, which increases the cost of manufacturing.
It would therefore be advantageous to have an ice making machine with a heat exchanger that has a lower pressure drop across it, as well as a velocity of the refrigerant that can be reduced to an optimal range.
It would be further advantageous to have a heat exchanger for use in a chiller or ice machine that can be made in an inexpensive manner.
It would be further advantageous to have a heat exchanger in which the refrigerant passageways allow for the refrigerant to come into a greater degree of thermal contact with the majority of the disk surface, to improve heat transfer.
It would be further advantageous to have a flat plate heat exchanger in which the outer walls were thin so as to provide high heat transfer, but were still able to withstand high pressures of the refrigerant.
Another need is to provide an ice making machine with flat plate heat exchangers that allow simultaneous scraping of several heat exchange surfaces with a single driving motor and little additional power for each additional surface.
There is yet a further need to provide a scraping mechanism for an ice making machine that is simple, robust and easy to service, and requires little clearance to service.